This invention relates to a vacuum or negative-pressure control valve, and more particularly to a negative-pressure control valve capable of outputting negative-pressure which is variable in response to variation of sensed or detected temperature.
As a negative-pressure controlling valve for vehicles depending on sensing or detecting of the temperature, a sucked-air temperature sensitive valve, a water temperature sensitive valve, an electromagnetic negative-pressure switching valve actuated by a temperature switch, etc., are provided in general. All of those valves are however operated only in two ways, that is to say ON or OFF. In various apparatuses incorporating this type of negative-pressure valve, such as an EXHAUST GAS RECIRCULATION controlling apparatus or system, a choke degree controlling apparatus, an ignition timing controlling apparatus, etc., a common disadvantageous weak point is difficulty of getting a steplessly continuous and smooth controlling feature sensitively variable in response to a timewise varied temperature which is detected by such a negative-pressure controlling valve. For example, the EGR controlling apparatus is required on one hand to raise EGR ratio, until the catalysis becomes active by the temperature rising after starting of the engine, for the purpose of restraining creation of nitrogen oxide (NO.sub.x). However, the EGR ratio must be on the other hand restricted not to go up, i.e., it must be held down to the necessary minimum in response to heating condition of the engine, because the rising of the EGR ratio is closely related to deterioration of the vehicle driving efficiency. Conventional way of EGR ratio controlling based on the actuation from a traditional negative-pressure controlling valve, which controls the negative-pressure only in two ways of ON or OFF by the temperature detection, is liable to give rise to a sharp or abrupt change of the EGR ratio either upwards or downwards according to whether the set temperature for the valve has been reached or not. It means that at least either one of the exhaust gas condition or the driving efficiency of the vehicle is obliged to be sacrificed in the vicinity of the border line of this set temperature.